The present invention relates to clay liners which are used to form a very low permeability barrier. The specific problem addressed by the present invention is how to create a seal between adjacent clay liners to provide a continuous and low permeability clay barrier.
A low permeability barrier is required in the construction of landfills in order to retain any liquid, known as leachate, contained within the waste material and keep the leachate out of the water table. Further, a low permeability bottom barrier is required in the construction of many man-made lakes and ponds to preclude water loss through seepage.
The use of bentonite to create a low permeability barrier in landfills and ponds is well known. Bentonite is a clay material which occurs naturally and it expands upon being exposed to or activated by water. When the bentonite absorbs water and expands, it is capable of forming a barrier with low permeability to fluid migration if the bentonite is properly contained.
Geosynthetic clay liners may be made with one or two sheets. The primary backing or carrier sheet is normally the more durable material and is often disposed below the bentonite layer when installed in the landfill. The cover sheet, also referred to as scrim, is normally less durable than the carrier sheet. Upon installation, the cover sheet may face up or down and the carrier sheet may face up or down, depending upon the specific design of the landfill. A layer of bentonite supported by at least one carrier sheet or disposed between two sheets (cover sheet and carrier sheet) is often referred to as a geosynthetic clay liner or GCL.
Workers will spread rolls of geosynthetic clay liners out over the area to be covered in a manner similar to the installation of carpet. In the past, in order to effectuate a seal between adjacent liners, it has been necessary to overlap adjacent rolls of liner material. In liners where the bentonite is suspended between two sheets by a needle-punching process, the seams must be augmented with granular bentonite, or other means, or liquids will leak downward at the seams created between adjacent rolls of liner material. The augmentation with granular bentonite (or other means) constitutes an extra installation step and therefore is costly in terms of time and money. Further, these seam augmentation procedures are dependant upon the construction crew following exacting installation procedures to effectuate a reliable seam.
In order for the activated bentonite to create a low permeability barrier, it must be properly contained. The bentonite may be contained between two sheets, a carrier sheet and a cover sheet. The bentonite may be held in place by glue applied to the carrier sheet or by needle-punching the cover sheet to the carrier sheet or by stitching the carrier sheet to the cover sheet or a combination thereof. The sheets may be manufactured from durable woven or non-woven materials or sheets that do not permit the bentonite to substantially migrate through the material. By properly containing the bentonite between two sheets that do not allow for substantial migration of the bentonite, the bentonite is properly contained and, upon activation by water, the bentonite will swell and form a low permeability barrier between the two sheets.
Depending on the construction of the fabrics or materials used, the lower or bottom sheet may not allow for the bentonite to migrate through to create a low permeability seam and simply overlapping adjacent liners may not insure that the proper seal will be attained between the two adjacent liners. In other words, laying an outer portion of the lower sheet of one liner on top of an outer portion of an upper sheet of an adjacent liner may not insure that a proper seal will be obtained between the two liners. In the case where the materials contained within the landfill include hazardous waste, a lack of a proper seal will result in leakage and will have serious ramifications.
Thus, there is a need for a bentonite clay liner, or a geosynthetic clay liner, that will ensure that a proper seal is obtained between two adjacent liners as the liners are installed in the bottom of a landfill or pond. Preferably, the geosynthetic clay liners should be self-sealing when adjacent liners are overlapped thereby insuring that no "seams" will leak and further providing a geosynthetic liner system that is quickly and efficiently installed.